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CCNA2 Chapter 4

CCNA2 Chapter 4. Learning about other Devices. Cisco Discovery Protocol (CDP). Neighbor Discovery with CDP

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CCNA2 Chapter 4

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  1. CCNA2 Chapter 4 Learning about other Devices

  2. Cisco Discovery Protocol (CDP) • Neighbor Discovery with CDP • Scenario: Assume your boss asks you to create a topology map of the network, including model numbers, IOS versions of Cisco equipment, etc. Now, suppose you are not in the building where the equipment is. You could use the Cisco Discovery Protocol (CDP) to gather information of directly connected Cisco neighbors. • CDP is: • Cisco proprietary (as the name indicates) • Operates at the Data Link layer • Functions regardless of what Physical layer media yu are using (fiber, UTP, etc) • Network layer routed protocol independent (IP, IPX, AppleTallk, etc) • Enabled on all Cisco devices by default • Sent as a multicast every 60 seconds out of all functioning interfaces, which enables neighbor Cisco devices collect information about each other.

  3. Cisco Discovery Protocol (CDP) • CDP is used to: • gather hardware and protocol information about neighboring devices • types of devices (switch, type of router) • router interfaces they are connected to • interfaces used to make the connection ( E0, S0, etc.) • model number of the devices • Best way to learn CDP is to do the labs!

  4. Cisco Discovery Protocol (CDP) When a Cisco device boots up, CDP starts up automatically and allows the device to detect neighboring devices thatare also running CDP. CDP runs over the data link layer and allows the two systems to learn about each other. Each device configured for CDP sends periodic messages, knownasadvertisements, to multiple Cisco routers

  5. Cisco Discovery Protocol (CDP) Primary use of CDP is to discover all Cisco devices that aredirectlyconnected to a local device. This is done by transmittingtype length values(TLVs)which are blocks of information embedded in CDP advertisements. To display the CDP information, use the command: show cdp Shows information that can be configured in Cisco devices: CDP timer - how often CDP packets are transmitted to all active interfaces CDP hold time – the amount of time that the device will hold packets received from neighbor devices

  6. Cisco Discovery Protocol (CDP) Merida# show cdp Global CDP information: Sending CDP packets every 60 seconds Sending a holdtime value of 180 seconds Sending CDPv2 advertisements is enabled Merida# show cdp neig Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone Device ID Local Intrfce Holdtme Capability Platform Port ID Internet Fas 0/0 168 R C2600 Fas 0/0 Vargas Ser 0/0 168 R C2600 Ser 0/0

  7. Cisco Discovery Protocol (CDP) • Device TLVs displayed by the show cdp neighbors include: • Device ID (hostname of device directly connected) • Local Interface (port or interface in which you received CDP packets) • Holdtime (keeps track of how long it has been since you received information from that neighbor and how many seconds to wait until you consider that neighbor dead) • Capability (router, switch, or repeater) • Platform (the model number such as Cisco router 2600, etc.) • Port ID (interface in which the neighbor device sent out the CDP information) • * Supported by Cisco IOS release 12.0(3)T or later

  8. Cisco Discovery Protocol (CDP) Sarasota# show cdp neighbors Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone Device ID Local Intrfce Holdtme Capability Platform Port ID Bradenton Ser 0/0 147 R PT1000 Ser 9/0 Miami Ser 1/0 148 R PT1000 Ser 9/0 Sarasota#

  9. Cisco Discovery Protocol (CDP) To enable CDPglobally: cdp run CDP is globally enabled by default. NOTE: on some switches (1900) cdp is not enabled To enable CDP on a particular interface, do: cdp enable On Cisco IOS Release 10.2 or higher, CDP is enabled by default

  10. CDP Exercise Create the topology in the graph Change the hostnames to Bradenton, Sarasota and Miami. Assign IP addresses with their respective masks: Bradenton Serial 9/0: 211.211.211.1 255.255.255.0 – clock rate 56000 Sarasota: Serial 0/0 211.211.211.2 255.255.255.0 Sarasota: Serial 1/0 200.200.200.1 255.255.255.0 – clock rate 56000 Miami: Serial 9/0 200.200.200.2 255.255.255.0 NOTE: You may have different numbers for your serial interfaces From the Sarasota router, issue a show CDP neighbors command. Your output should look like the one from slide 8

  11. Cisco Discovery Protocol (CDP) • NOTE: • Disable CDP at the global level withno cdp run • If CDP is disabled globally, individual interfaces cannot be enabled for CDP • IOS Release 10.3 or higher, CDP is enabled by default. • To disable CDP on a specific interface after it has been enabled:no cdp enable

  12. CDP Exercise 2 (Dissable CDP in local interface) • Test this with the Sarasota router. • (You must be in that interface first.) • Sarasota(config)#int s1/0 • Sarasota(config-if)#no cdp enable • Issue the following command, and you’ll see info coming form interface…..? • Sarasota#show cdp neig • Now, put it back the way it was • Sarasota(config)#int s1/0 • Sarasota(config-if)# cdp enable • Sarasota#show cdp neig • Sarasota#show cdp neig

  13. CDP Exercise 3 (Dissable CDP globally) • Test this with the Sarasota router. • Sarasota(config)#no cdp run • Issue the following command, and you’ll see info coming form interface…..? • Sarasota#show cdp neig • Now, put it back the way it was • Sarasota(config)# cdp run • and check it again • Sarasota#show cdp neig

  14. Clear cdp counters Useful for resetting interface statistics on a Cisco router

  15. Show cdp

  16. Show cdp entry

  17. Show cdp interface Status of the carrier detect signal Keepalive messages

  18. Show cdp neighbors Know this output! Router#show cdp neighbors detail will also give the IP address of the neighboring Cisco device

  19. Telnet Telnet is a virtual terminal protocol that is part of the TCP/IP protocol suite. Provides a remote login capability. Telnet function is at theapplication layer. If a telnet command is successful from one device to another, then all 7 layers of the OSI model is ‘working’. Cisco says- It is the most complete testing mechanism available. Telnet uses the five (5) vty sessions. There has to be a ‘login’ and password associated with the vty session in order for telnet to work. If a Telnet session is left open for 10 minutes without activity, it will automatically close itself.

  20. Reopening a suspended Telnet session • Multiple Telnet sessions can be used and suspended by using the Ctrl-Shift-6, then x sequence. • The session can be resumed by pressing Enter. • Pressing the Enter key causes Cisco IOS to resume themost recentlysuspended session. • Theresumecommand can be used to start up a previous session, but must knowthe connection ID. • Use the show sessions command to get the connection ID,then resume the correct session.

  21. Reopening a suspended Telnet session It works with Packet Tracer!

  22. Telnet • If there is a ‘host table’ on the router (ip host <name> <ip add>), then you can dotelnet <host name>. • As an example: • telnetrouterB • DO THE LABS FOR resuming and suspending SESSION. • NOTE: • Pressing Enter takes you to the most recent session • To resume a session it needs a connection ID.

  23. Ping Ping command is used to determine if a particular ip address is reachable. Traceroute command is used to trace the route to an ip address. Ping sends ICMP echo request messages and receive an echo reply. Ping Command CodeExplanation ! ICMP echo reply received . Nothing received U ICMP unreachable (destination) received N ICMP unreachable (network) received P ICMP unreachable (port) received

  24. Interface Protocol Serial is up, line protocol is up operational Serial is up, line protocol is down Connection problems (L2) Serial is down, line protocol is down Interface problems (L1) Serial is administratively down, line protocol is down Manually disabled

  25. Interface Protocol • For serial port: • Serial is up, line protocol is downmaybe caused by: • network mismatched • clock rate not set on DCE • mismatch of encapsulation (HDLC vs. PPP)

  26. Key terms Hostname hostname Ip host hostname IP Ip domain-lookup no ip domain-lookup Exec-timeout minutes seconds show cdp neighbors show cdp neighbors detail cdp run cdp enable telnet IP_address

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